<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>

    <!--从 CDN 引入 vue.js -->
    <script src="https://unpkg.com/vue"></script>
</head>
<body>

    <div id="app">
        <input type="text" id="input" v-model="msg" />
        <div id="box" >
            {{msg}}
        </div>
    </div>


    <script>
        let app = new Vue({
            el:"#app",
            data:{
                msg : ''
            }
        });
    </script>

</body>
</html>